1. Field of the Invention
This invention relates to a porous sheet material useful for the affinity chromatographic and/or ion-exchange chromatographic separation and purification of biological substances, as a biochemical reactor, and as a battery separator; processes for manufacturing such sheet material; methods for using such material; and apparatus in which such material is employed.
2. Statement of Related Art
Recent advances in biochemistry, molecular biology and like disciplines have required faster and more accurate techniques in the recovery, purification and analysis of small amounts of biological substances such as DNA segments and proteins. Methods such as ion-exchange, affinity, and other chromatographic separation processes all have required as a necessary step the separation and recovery of these biological materials from gels, broths, or like media, conventionally using either various types of adsorption columns such as ion exchange columns, affinity-binding techniques and the like. More recently, an alternate method for recovering DNA or proteins from gels comprising electrophoretic separation has been provided which involves dissolving the desired gel slice in chaotropic salts, such as sodium iodide (NaI), followed by selective binding of the DNA to glass beads, i.e. a suspension of silica matrix in water, which is then subjected to centrifugation. Proc. Natl. Acad. Sci. USA, 76 No. 2, pp. 615-619 (1979).
U.S. Pat. No. 3,862,030 discloses a material useful as a microporous fluid-permeable filter medium comprising a polymeric resinous matrix such as polyvinyl chloride (PVC) having an inorganic filler dispersed throughout, in particular silica. U.S. Pat. Nos. 4,102,746, and 4,169,014, disclose like compositions in which the silica has been activated by the addition of binding groups, i.e. active ligand sites.
U.S. Pat. No. 3,922,432 teaches a hydrated gel sheet having incorporated therein or bonded thereto a layer of particles having an affinity for selected materials to be separated from a mixture containing the same. Included among these affinity-binding particles are such materials as hydroxypropylcellulose, diethylaminoethyl (DEAE) cellulose, microcrystalline cellulose and the like. This composition is a non-porous material which permits no flow-through of liquids, only surface contact with the scored sheet, as described therein.
Moreover, as taught in Affinity Chromatography, pp. 36-37, [Wm. H. Scouten, John Wiley and Sons, N. Y. publ. (1981)] there are two problems associated with the use of cellulose as an affinity-binding matrix: (1) it is fibrous in nature, and thus easily clogged; more significantly, it is easily compressed, even at moderate pressures; and (2) it is often contaminated with a wide variety of impurities, which must be removed before use.
U.S. Pat. Nos. 4,373,519; 4,460,642; 4,565,663; and 4,722,898, each disclose a composite sheet material comprised of a polytetrafluoroethylene matrix having enmeshed therein hydrophilic absorptive particles such as cellulose, dextran, clay or the like for use as a wound dressing or as a chromatographic material.
Similarly, U.S. Pat. No. 4,705,809 describes a porous thermoplastic article for use as a filter, battery separator, or film, in which the thermoplastic comprises a non-water soluble thermoplastic compound and water-soluble cellulose, hydroxyalkyl cellulose or derivatives thereof, admixed therein. The cellulose employed in this patent is intentionally water-soluble, e.g. a hydroxycellulose compound, and is substantially washed out of the matrix to create the desired pores, thus leaving only a small residue of cellulose in the final composition.
U.S. Pat. No. 4,663,163 describes a swellable, modified polysaccharide material comprising a fibrous polysaccharide which is chemically bonded covalently to a polymerizable compound which contains a variety of chemical groups possessing both covalent bonding and chemically binding functions, i.e., wherein the latter are ionizable, thereby forming a chemically unitary composition useful for chromatoqraphic procedures. U.S. Pat. No. 4,743,373 describes a complex chromatographic device which can employ, inter alia, the swellable, fibrous material of U.S. Pat. No. 4,663,163.
U.S. Pat. No. 4,385,991, as well as corresponding British Patent 1,600,241, defines deformable, ampholytic gels containing polysaccharides, wherein said gels are impregnated in discrete, particulate materials such as diatomaceous earth or the like for use in chromatographic separations, etc.
The publication "A Unique Flow Through Microporous Chromatography Device for Protein Purification", Goldberg et al., AICHE Biotechnology Conference, N.Y., Table I, (Nov., 1987), teaches that it is conventional to use such materials as a diethylaminoethyl-activated cellulose alone, or a microporous polyvinyl chloride (PVC) sheet containing silica reacted with polyethyleneimine (PEI), for use in ion exchange chromatography for binding and purifying proteins.
FMC Corporation, Philadelphia, Pa., under the ACTI-DISK and ACTI-MOD trademarks, sells products containing microporous PVC sheeting having silica particles dispersed throughout, which particles may be activated for anion/cation exchange chromatography with polyethyleneimine (PEI), sulfopropyl (SP) or carboxymethyl (CM) and for affinity chromatography with glutanaldehyde (GTA), r Protein A, or r Protein G. [FMC BioProducts 1989 Price List, p. 11].